1. Field of the Invention
This invention relates generally to a compact, portable resistance heating device, and more particularly to a compact, portable resistance heating device for heating and stretching a rod or post, such as a stud or threaded bolt, on a steam turbine casing, a heat exchanger, or the like.
2. Description of the Related Art
Commonly, a bolt heater is used to fasten or loosen a bolt or stud used on steam turbine casings or the like that cannot be fastened or loosened by a wrench or spanner whereby the bolt heater raises the temperature of the bolt or stud by subjecting it to an alternating current electricity. The alternating current flowing from the bolt heater induces eddy currents in the bolt or stud and the resistance leads to Joule heating causing the bolt or stud to be become heated and stretch or elongate. Typically, the depth to which the eddy currents penetrate, and therefore the distribution of heat within the bolt or stud, depends on the frequency of the alternating current and the magnetic permeability, as well as the resistivity, of the bolt or stud. During this process, the bolt or stud will elongate or stretch due to expansion during heating, thereby allowing a nut to be threaded onto the bolt or stud to a greater degree during the fastening operation. As the bolt or stud cools and shrinks, the nut is pulled tautly against the surrounding surface of the turbine casing or heat exchanger. This process ensures a secure and firm connection of the nut on the bolt.
For removal of a bolt or stud, such as during servicing of the turbine or heat exchanger, the reverse process is followed. The bolt or stud is heated causing it to stretch, and in so doing, the nut moves away from the surrounding surface and lessens the force holding the nut against the surrounding surface of the turbine casing or heat exchanger.
Known resistance type bolt heaters operate at 240 volts or 480 volt, three-phase alternating current. Typically, these known bolt heaters are individually controlled and require five minutes or more to sufficiently heat and stretch each bolt for fastening or removal. In addition, these known resistance type bolt heaters require close tolerances between the axial bore of the bolt or stud and bolt heater. Further, the power output of these known resistance type bolt heaters cannot be varied and the bolt heaters cannot be removed from the bolt prior to cooling. If these known resistance type bolt heaters are removed from the bolt prior to cooling, the bolt heater will overheat and burn out because the produced heat is not dissipated. Furthermore, these known resistance type bolt heaters are not capable of being bent or shaped to fit the user's particular need.
It is therefore desirable to provide a compact, portable resistance heating device capable of heating and stretching a plurality of bolts or studs simultaneously regardless of the diameter of the bolt or stud.
It is further desirable to provide a compact, portable resistance heating device capable of heating and stretching a plurality of bolts or studs that do not have an axial bore or that have an axial bore either individually, in totality or a combination thereof.
It is still further desirable to provide a compact, portable resistance heating device that is sufficiently portable, compact and lightweight so as to be easily movable by a single user on a turbine deck, a deck of an oil refinery or the like.
It is yet further desirable to provide a compact, portable resistance heating device that does not require a cooling fluid, hydraulic pumps or air hammers during operation.
It is yet further desirable to provide a compact, portable resistance heating device having a selectively variable output power range from 0 to 100%.
It is yet further desirable to provide a compact, portable resistance heating device that utilizes a cartridge heater having a heating element that is not limited by clearance between the axial bore of the bolt or stud and the heating element.
It is yet further desirable to provide a compact, portable resistance heating device that utilizes a cartridge heater having a heating element that is capable of being bent or shaped.
It is yet further desirable to provide a compact, portable resistance heating device having a plurality of cartridge heaters that are capable of operation either individually or a combination thereof.
It is yet further desirable to provide a compact, portable resistance heating device capable of heating and stretching a bolt or stud in under five minutes time.
It is yet further desirable to provide a compact, portable resistance heating device that reduces man hours and outage times.